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प्रश्न
विकल्प
40 cm
25 cm
`1/40` cm.
`1/25` cm
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उत्तर
The power of a convex lens is 2.5 dioptres. Its focal length is 40 cm.
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संबंधित प्रश्न
An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre 'O' of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical 'O', principal focus F and height of the image on the diagram.
When a ray of light enters from one medium to another having different optical densities it bends. Why does this phenomenon occur?
A beam of light travelling in air is incident of water. Draw a ray-diagram indicating the change in its path in water.
Describe with the help of a ray diagram the nature, size and position of the image formed when an object is placed in front of a convex lens between focus and optical centre. State three characteristics of the image formed.
What kind of lens can form:
an erect magnified image?
A camera fitted with a lens of focal length 50 mm is being used to photograph a flower that is 5 cm in diameter. The flower is placed 20 cm in front of the camera lens.
At what distance from the film should the lens be adjusted to obtain a sharp image of the flower?
A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm
In a certain murder investigation, it was important to discover whether the victim was long-sighted or short-sighted. How could a detective decide by examining his spectacles?
A lens forms an inverted image of an object. Name the kind of lens.
A lens forms an upright and magnified image of an object. Name the lens.
If you are to determine to focal length of a convex lens, you should have
(A) a convex lens and a screen
(B) a convex lens and a lens holder
(C) a lens holder, a screen holder and a scale
(D) a convex lens, a screen, holder for them and a scale
State two applications of a convex lens.
What is the difference between a double convex and a bi-convex lens?
State the position of object, position of image, nature of image when: Convex lens is used as objective lens of astronomical telescope.
Write the three characteristics of the image formed by a convex lens of focal length 20 cm for the object at distance (i) 10 cm, (ii) 30 cm, (iii) 40 cm, (iv) 60 cm from the lens.
In the figure given below L is a convex lens, M is a plane mirror and S is a point source of light. Rays of light from the source S return to their point of origin. Complete the ray diagram to show this. What is the point S called?
We can burn a piece of paper by focussing the sun rays by using a particular type of lens. Name the type of lens used for the above purpose. Draw a ray diagram to support your answer.
Distinguish between:
Concave lens and Convex lens
